Of these fuel cell types at least PEM fuel cells, which are fed with hydrogen or with a hydrogen-rich synthesized gas, require a certain relative humidity at the hydrogen side of the fuel cells in order to be able to operate. For this reason it has previously been customary to provide a water container at the anode side of the fuel cells which delivers water to the humidifying device for the humidifying of the hydrogen gas.
Furthermore, similar humidifying devices are provided at the cathode side of the fuel cells and ensure that the oxygen (normally in the form of air) supplied to the fuel cells at the cathode side of the fuel cells is appropriately humidified. The humidifying of the gases at both the anode side and at the cathode side is above all necessary when starting up the operation of the fuel cells. In the operation of the fuel cells water is produced and takes care of the necessary humidification of the corresponding gases, as will later be explained in more detail in the description of embodiments. The humidifying devices are thus in principle only required when the fuel cells are taken into operation in order to positively influence the starting behavior of the fuel cells. The provision of the corresponding water containers is, however, problematic, because at temperatures below zero attention must be paid that the water contained in the water containers does not freeze. Proposals have already been made relating to the omission of the water containers and humidifying devices.
Even when humidifying devices are omitted, a problem exists, and indeed that the water present at the cathode side and at the anode side of the fuel cells, which forms in operation, condenses during cooling of the fuel cells and forms water droplets. A pronounced danger exists that at temperatures below zero the water droplets which separate out in this way freeze and, in operation or on recommencing the operation of the fuel cells, at least partly hinder the gas flow through the relevant, frequently narrowly dimensioned, passages and chambers.
Ice formation of this kind can hinder or prevent the throughflow of hydrogen and/or atmospheric oxygen, so that the operation or a renewed commencement of operation of the fuel cell system is prevented or only starts up very slowly. Moreover, the corresponding gases are not humidified, because the water has separated out in the form of ice. The lack of humidification of the gases can lead to the membranes in the PEM fuel cell being damaged.